1. Technical Field
This disclosure relates to magnetic write heads that write on magnetic recording media, particularly to the fabrication of their magnetic coils that create the magnetic fields for writing.
2. Description
As hard disk drives have been increasing the recording density of the magnetic disks on which data storage occurs, the thin-film magnetic heads used to write and read that data have been required to improve their performance as well. The thin-film read/write heads most commonly in use are of a composite type, having a structure in which a magnetism detecting device, such as a magnetoresistive (MR) read sensor is used together with a magnetic recording device, such as an electromagnetic coil device. These two types of devices are laminated together and serve to read/write data signals, respectively, from/onto magnetic disks which are the magnetic recording media.
In general, a magnetic recording medium, on a microscopic level of composition, is a discontinuous body in which fine magnetic particles are assembled and held in place in a matrix. Each of these fine magnetic particles has a single magnetic-domain structure, so one recording bit is actually formed by a plurality of neighboring particles. In order to enhance the recording density, therefore, it is necessary to make the magnetic particles smaller in size so as to reduce irregularities at the boundaries of the bits. As the particles are made smaller, however, their volume decreases, so that the thermal stability of the magnetization may deteriorate. This causes a problem.
An index of the thermal stability in magnetization is given by KUV/kBT. Here, KU is the magnetic anisotropy energy of a magnetic fine particle, V is the volume of one magnetic fine particle, kB is the Boltzmann constant, and T is the absolute temperature. Making the magnetic fine particles smaller just reduces V, which lowers KUV/kBT by itself, and thereby worsens the thermal stability. Though KU may be made greater at the same time as a measure against this problem, the increase in KU also increases the coercivity of the magnetic recording medium. However, the writing magnetic field intensity produced by a magnetic head is substantially determined by the saturated magnetic flux density of a soft magnetic material constituting a magnetic pole within the head. Therefore, there can be no writing if the coercivity exceeds a permissible value determined by the limit of writing magnetic field intensity.
One method proposed for solving such a problem affecting the thermal stability of magnetization is the so-called thermally assisted magnetic recording (TAMR) scheme. In this approach, heat is applied to a magnetic recording medium immediately before applying a writing magnetic field, particularly while using a magnetic material having a large value of KU. The heat then effectively lowers the medium's coercivity at the same position where the magnetic writing field is applied, so as to enable writing as though it were on a medium with lowered coercivity.
This scheme is roughly classified into magnetic dominant recording and optical dominant recording, depending on the relative effects of the magnetic field and the optical heating. In magnetic dominant recording, the writing is attributed to the localized effects of the electromagnetic coil device, while the radiation diameter of the incident light is greater than the track width (recording width). In optical dominant recording, by contrast, the writing is attributed to the light-radiating effect, as the radiation diameter of the incident light is substantially the same as the track width (recording width). Thus, the terms “magnetic dominant recording” and “optical dominant recording” impart the effects of spatial resolution to a magnetic field or a radiation field, respectively.
In the thermally assisted magnetic head recording apparatus, a light source such as a semiconductor laser is typically suggested as the source of thermal energy. Light from a light-emitting device is introduced into an optical waveguide. As waveguide material, TaOx or SiON is proposed. The waveguide is surrounded with cladding material, typically Al2O3, SiON or SiO2. The light is focused by a plasmon generator at the distal end of the waveguide, which is usually made of highly conductive material such as Au or Ag. There are many kinds of plasmon generators. The light focused at the plasmon generator is emitted, as plasmon energy, from a light exit and heats the surface of recording media.
As indicated above, thermally assisted magnetic head recording is a new technology for use in a future (HDD) hard disk drive head to achieve higher recording density. To maximize the effectiveness of this technology, the frequency extendibility (range) of the HDD head needs to be improved at the same time. The most effective method to improve frequency extendibility is to shorten the magnetic path of the recording flux. One way to do this is to make a smaller pitch coil.
The prior arts teach several methods to address the problems of improving coil structure and performance. Hsiao et al. (U.S. Pat. No. 7,313,858), Lee et al. (US Publ. Pat. Appl. 2006/0065620) and Dinan et al. (U.S. Pat. No. 7,117,583) all address issues of coil structure, but none provide a method to produce the desirable effects of the present disclosure.